The present invention relates to a radio transceiver including an antenna switching circuit and, more particularly, to an antenna switching circuit capable of changing reception sensitivity.
In a radio transceiver of the type described, it has been customary to selectively connect a transmitter and a receiver to an antenna by an antenna switching circuit which is responsive to a transmission/receipt control signal and comprised of diodes and others, thereby transmitting or receiving such a radio signal as a frequency modulated signal. Such a transceiver is proposed in the European Patent Publication No. A2-0151014 published in Aug. 7, 1985 and assigned to NEC Corporation.
A prerequisite with a radio transceiver having the above construction is that two remote transceivers, which are in communication, are free from the interference of alien signals. An implementation heretofore adopted to meet such a requisite is varying the gain and, thereby, the reception sensitivity by changing the current value (e.g. emitter current value) of a transistor which is installed in the receiver for high frequency amplification (RF AMP).
However, such a prior art implementation suffers from a drawback that when the current of the transistor for RF AMP is reduced, the transceiver becomes susceptible to mutual interference and, in addition, the decrease in the bias emitter current may deteriorate the temperature characteristic.